1. Field of the Invention
The present invention relates to an internal combustion engine which is cooled by a so-called boiling liquid cooling system, and more particularly to an improved cylinder head for such engine wherein coolant is introduced thereinto in liquid state and exhausted therefrom to a heat exchanger in a gaseous state.
2. Description of the Prior Art
Hitherto, there has been proposed a so-called boiling liquid cooling system (viz., evaporative cooling system) for cooling an internal combustion engine. This type cooling system basically features an arrangement wherein a liquid coolant (water) in the coolant jacket of the engine is permitted to boil and the gaseous coolant thus produced is passed out to an air-cooled heat exchanger or condenser where the gaseous coolant is cooled or liquefied and then recirculated back into the coolant jacket of the engine. Due to the effective heat exchange effected between the gaseous coolant in the condenser and the atmosphere surrounding the condenser, the cooling system exhibits a very high performance. European Patent Application No. 0,059,423 published on Sept. 8, 1982 discloses one of the above-mentioned cooling systems.
However, some of the prior art systems hitherto proposed have suffered from a drawback, due to their inherent construction of the cooling jacket formed in the cylinder head of the engine, in that when the attitude of the engine changes with respect the horizontal (which occurs, for example, when the vehicle is traversing a steep hill or inclines), the coolant tends to move toward a lower side of the jacket thereby to leave a heated portion of the engine uncovered and/or insufficiently covered with the coolant. This drawback will be well understood from FIGS. 2 and 4 which show respectively the undesired conditions of FR (front engine rear drive) (see FIG. 1) and FF (front engine front drive) (see FIG. 3) motor vehicles, each being equipped with the boiling liquid cooling system. The engine of FIG. 2 is of a gasoline type, while, the engine of FIG. 4 is of a diesel type.
As may be understood from the drawings, the undesired condition tends to permit a dry zone to form in the coolant jacket. This dry zone, due to the apparent lack of coolant, becomes highly heated and further promotes the "dry-out" phenomenon, so that engine knocking and/or thermal damage of the engine tends to occur. This problem becomes quite severe in case of the diesel engine because the pre-combustion chambers thereof are excessively heated during the operation thereof.